The Principality of Sealand (http://en.wikipedia.org/wiki/Principality_of_Sealand) calls itself a country even though it isn't recognised by any country (although it claims recognition from the UK and Germany). Despite the fact it's just an oil rig, would it ever be possible to make a WarLight map of Sealand, or would that be a stupid idea?

That depends what your definition of the word country is, since it's a general use word rather than 1 with an official definition. If you're using the word country to mean sovereign state with international recognition, then yes, Sealand is not a country. I called this thread "Could this 'country' ever be a WarLight map?" instead of "Could this country ever be a WarLight map?" for a reason.